Telephone system



June 10, "1930. '5, 'A 1,763,013

' TELEPHONE SYSTEM Filed July 3, 1929 I 3 Sheets-Sheet 1 l I INVENTOR v 4770mm June 10, 1930. T. s. SKILLMAN 1 ,763,013

TELEPHONE SYSTEM Filed July 5, 1929 s Shets-Sheet 2 FIG-4.

' ATTORNEY Patented June 10, 15930 UNITED S ES OF NEW YORK TELEPHONE s sTn Ap lication filed July a, 1929, Serial No. 375,715,. and in Great Britain, July 20, 1928; c.

p V v A g L A This invention rela-testotelephone systems. In known telephone systems in which repeaters are provided for insertion into the lines which may require them, it is usual that-either a repeater or a group of repeaters are 7 permanently connected with the lines or that the insertion of the repeaters is controlled manus ally by an operator. In a further development however the insertion ofthe repeaters in theline maybe effected partially bysennautomatic means as may be seen from U. S.

Patent No. 1,708,982 Serial No. 39,882filed' 27th June, 1925.

Among the disadvantages of systems of this type heretofore proposed was the impossibility of their ready adaption to purely automatic systems and one of the main objects of this inventionisto overcomethis limitation though as will be mentioned later the present which the marking of a contact is efifectedby -establishing an alternating potential vdifference between saidcontact and the said movable member whereby when, said movable member reaches said marked contact a current is caused to flow in an associated circuit caus-I ingsaid movable member to stop on said marked contact.

A feature of the invention resides in the means provided for arresting the said movable member on said worked contact which means may compr se a transformer the secondary winding of which is connected in series with the said movable member so that y when said member reaches the said worked contact, the said'secondary w nding is short which is suflicienttooperate a relay connected in the circuit of said primary winding. Obviously other means than a transformer can be used for this purpose, for instance the scheme may also have advantages when used v oircuited thusoausing an increase of current in the primary winding of said transformer above mentioned relay may be directly conn'ectedm the circuit of sald'movable member. However the provision of a transformerused PATENT est-roe THOMAS SAMUEL SKILLMYAN, on ALDWYCH, LoNDoN, ENGLAND, ASS'IGNOR, TO wnsr- ERN ELECTRIC COMPANY, INCORPORATED, or ew YORK, N. Y., A CORPORATION in the manner pointed out above is considered .a Valuable feature of the present invention;

'A feature of the presentinvention is a system in which a repeater may be insertedinto a line entirely automatically and according to the requirements of the line. 7 f l According to another aspect the invention maybe regarded as a telephone systemin" which an established connection between two polnts 1s utilized for transmitting current for determining whether or not arepeater should be interconnected there betweem this discrimination being utilized for automatically governing the insertion of a repeater.

According to anotherfeature of the invenover the talking-circuit for. controlling the tion an alternating current is transmitted automatic insertion of a repeater in said circuit. v I

In accordance with still another feature of'the' present invention an alternating" current is transmitted over the talking circuit to determine whet-her or not a repeater should be interconnected in said circuit. For the above purpose advantage may be taken of the actual attenuation of thetransmission circuitor alternating currents. having a characteris tic depending upon the attenuation of the.

transmission circuit may besent thereover, means being provided responsivezto said alternating. cur'rentsfor governing the insertion of a repeater inthe transmission circuit.

By using a combination of signals depend mg upon the mdivldual transmission equivalent of the lines it is possible to initiate the selection and the insertion of a repeater in the'circuit only if thecombined transmission equivalent of the interconnected lines neces- I sitates a repeater.

According to a further feature of the in-.

vention a discrimination is made between the nature of a plurality of lines (e. g. theirattenuation characteristic or whether they are short orlong lines etc.) by meansof alternate mg current of difl'erent frequencies orof altern atmgcurrent ofdlfi'erentamplltude or of i alternating current modulated or interrupted at different speeds.

A further feature of the invention provides facilities for using any one of a group of lines for repeater working and at the same time picking up one of a preferably much smaller group of balancing networks.

According to another feature or modification a system is provided in which the connection of cord circuit repeater is controlled entirely by the line equipment and the repeater equipment so that any form of manual cord or automatic switch may be used in the connection.

According to another feature of the invention the line equipment individual to the transmission lines are adapted to perform the function of signalling that is to say to transmit dial impulses ringing currents etc. and also to control the insertion of a repeater in the transmission circuit. This is a very important feature of the present invention.

Another feature of the present invention resides in the provision of means for gain regulation which may be efiected by means of an alternating current (e. g. voice frequency) transmitted over the signalling circuit for controlling the gain of the amplifier.

Alternatively the gain of the repeater interconnected in the line may be controlled by means of a plurality of marginal relays or by means of attenuating pads adapted to be inserted in the circuit.

Other features of the invention will appear from the following description.

In the accompanying drawings:

Fig. 1 shows the signalling and line equipments at the incoming end of a toll line;

Fig. 2 shows an operators cord circuit;

Fig. 3 shows the signalling and line equipments at the outgoing end of a toll line.

Fig. 4 shows the equipment associated with I the repeater.

Fig. 5 shows schematically an arrangement embodying the invention for switching a toll line L1 to a toll line L2 over automatic switches S1, S2 and S3; 7

Fig. 6 shows schematically the working system according to the present invention.

Fig. 7 shows a method of applying the invention for controlling a repeater over a junction circuit.

In the drawings Figs. 1 show the detailed circuit of a particular embodiment of the invention and Figs. 5 and 6 are simplified diagrams illustrating the working of the circuit.

Considering first Fig. 5, this shows equipment located at a central otfice upon which converge a number of long telephone lines referred to as toll lines. These toll lines are used for traffic into and out of the control of fice and its local area, and are also used for traffic through this area. In the latter case two or more toll lines will be connected in tandem, and since in most cases this will cause a high attenuation of the speech currents, a repeater will be necessary between the two lines.

General In Figure 5 two such lines L and L are shown connected together by means of a finder switch S and selectors S and S These willbe controlled by dialling impulses received over the line either directly or by means of a register such as It which is connected by the circuit 0. Alternatively an operators cord circuit may be used to connect the two lines L and L TLl and TLO represent the special line equipment necessary to control the insertion of the cord circuit repeater. They are individual to each line.

In the detailed circuit which illustrates the invention it is assumed that these equipments TLl and TLO are used also for signalling over the lines themselves and a simple arrangement is shown combining the two functions. It should be pointed out however that the use of the signalling apparatus for controlling a repeater, although a valuable feature, is not essential, and separate equipment for the repeater control may be used.

The equipment TLl and TLO may include devices responsive to alternating current, such as vacuum tube detectors, or voice frequency relays. Signalling between TLl and TLO is used to decide whether a cord circuit repeater is necessary, the alternating current devices discriminating between alternating currents of diflerent character which are transmitted between TLl and TLO over the talking circuit. In the embodiment of the invention which is shown in Figs. 1-4: voice fre quency relays are used, and the discrimination is obtained by using different frequencies, but alternative methods such as the use of diiferent amplitudes or of interruptions at different speeds will readily occur to those skilled in the art.

The exact sequence of operations whereby TLl and TLO signal to each other to determine whether a repeater shall be connected may be varled considerably to suit individual cases. The preferred arrangement is for TLO to send a pulse signal to TLl and if this signal is such that a repeater is needed TLl initi ates the operation of connecting the repeater. This pulse may be sent at any time when a talking circuit between the two line equipments is assured and the simplest way of providing for this is to wait until the called subscriber replies, since a talking current between TLl and TLO will always be present at this time whether manual or automatic connections are used. The attenuation of the two lines for operators conversations occurring before the subscriber replies will not be excessive, owing to the absence of subscriber loops and the slight delay before the called subscriber isv able to talk, would not be noticed. j

' An alternative arrangementwould be for TLO to send out tone continuously until the peaters may beallowed to hunt simultanecalled subscriber replies,- and for TLl to respond to this and to pickup the repeater; In automatic equipment where the talking cir-' cuit could easily be made continuous by the addition of suitable small condensers TLO could send. out a pulse or pulses immediately it is picked up and this would be sure-to reach TLl, but where operators may interrupt the connectnig circuit this cannot be done. An-

other plan would be for T L1 to send a pulse ora continuous tone to TLO and for TLO to pickup the cord circuit repeater firstQ. ()ther arrangements such as starting the signal from TLO by a preliminary pulse from TLl reccived only when the connection is completed, will readily occur to those skilled in the art and need not be elaborated.

Returning however to the preferred method of signalling between the line equipment, it is assumed that TLO. sends a signal to TLl to initiate the insertionof the repeater. If

TLO is a line of highattenuationwhich will require a repeater whencver connected to another toll'line, a signal (B) will be sent... If,

however, it is a comparatively short line with low attenuation a repeater may be needed only when otherlinesof high attenuation are connected and in this case TLO sends out a signal (A). The equipment inTLl will be arranged to respond therefore either to signal (B) or to signals (A) and (B) depending on the attenuation of the Line L and thus discrimination is obtained between connections which require repeaters and connections which do not.

Connections which do require repeaters maythemselves require differentgains and the arrangements for providing this are described later. p

The response of the apparatus TLl causes it to pick up a free repeater over the line finders LF and LF (for smaller groups of lines, of course, only one. finderwill be. required). The repeater apparatus REP must then pick up the line L over the finders LF and LF and special arrangements will be needed to do this since it'will not be normally-possible to provide a special markingcir'cuit over the automatic switches or the cord circuit connecting TLl and TLO. It would of course 1 be easy to do this by. providing special cord 7 circuits or special. automatic switchesbut such an arrangement is extremelyuneconomical,'in view of the small numberofconnec-.-

' N is connected to the network circuit of the repeater, whilst 0 and 0 are the test brush tions which require cord circuit repeaters. Accordingly the marking of L from REP is carried out over LF LF TLl S; C S

, a a v 9 circuit will always exist between these two points. I

An arrangementis described inconnection with Figs. 1 to 4 whereby 'a'number of; re-

ate the relay and thus to operate a direct cur-' rent relay to stop the switch. It is obvious that the short circuit can only be elfecti-ve' overthe correct connection and not over'cross connections. InZcases where preventionof cross connection. is not required, as in very small offices, the voice'frequencyrelay may be connected-directly in theta-lking circuit.

' As several vtypes'of toll lines L1- and L2 maybe connected to the repeaters it is necessary to provide-balancing networks Nl.'ancl. N2 suitable for balancing each type of toll- This is achieved in the arrangement-of line. Fig. as follows :-.As soon as the cord circurt repeater has picked up. aline, a suitable balancing network is also picked up over NFl or NF 2. Automatic methods known in the art may be applied to this, a

simplified arrangement being shown dia grammatically in Fig. 6 and in detail in Fig.

well 1 4. Referring to Fig. 5 all the. toll lines which requires. similar networks are ar-- ranged to marka commontermlnal in net work finders NFl onNFQ, which are associated with the corresponding group of networks. An individual network of the group is then Picked up by the network finderxy) i w It will be seen that trouble. from cross connection may. arise in the. network selec- This may be overcome. either by using tion. 7 the volce frequency selection already pro vided for in the repeater or by any well:

known method used in automatic telephony. For instance a master switch may be'provided for distributing the cord circuit re-:

peaters, thus only permitting one repeater to hunt at a time.

More specifically in Fig. 6 the banks of contactsof line finder vLFand of network finder NFl are shown. A group of toll lines such as L, connected to line finder LF are dividedinto groups, for instancein three groups A, B, C, to which correspond on the network finder NF three groups A 13 ,0 of suitable balancing networks; In this fig ure L leads to the line circuit of the repeater,

Marking potential applied by way 'of GMl fromthe repeater enables NF to pick up the required group of networks by means of;

brush GM2 and then to select an idle network by means of brush O Returning to Fig. 5, the stage has now been reached where L and L are connected by way of the repeater REP, and balancing networks N and N for these lines have been picked up. The switching apparatus associated either with REP or with TLl or TLO nowoperates to release the switches S S and S and conversation may then proceed in the normal wayover the repeater. Release of the repeater may be controlled from the distant end by means of TLl or by a local operator, where the original connection was completed manually.

In large areas, such as the London area, incoming and outgoing toll lines may be located in diflerent places through calls being connected either manually or automatically over a junction circuit. It will be clear that in this case the arrangements described above may be used. A typical instance is shown in Fig. 7 in which a repeater may be connected in series with the existing connections instead of in shunt.

As before signalling between the line equip ment of the incoming and outgoing lines is carried out over the talking circuit and a repeater is connected when required. In such a case difficulties will arise in balancing the line connected to the junction circuit. This will be so however on any method of working over a junction circuit and is not related to the present invention.

Fig. 7 shows a method of working over a junction circuit utilizing the principle of controlling the repeater connection by the line equipment and using the interconnecting talking circuit to provide signalling between the line equipments. The operation of the arrangements of Fig. 7 is as follows L1, L2, TLi, TLO, s3, s1, s2, 0, N1,-LF1, LF& and REP are the same as before. L2 however is now reached over a junction circuit and switch S4 and the repeater REP is connected in series with the connection. A

- compromise network N2 is used for balancing the line over LF. Sl/Vl and S W2 are relay groups to introduce the repeater. Signalling between TLl and TLO takes place as before and TLl picks up the repeater.

Other-modified methods of applying the same principles for connecting the repeater into the circuit will occur to those skilled in the art.

Turning now to the circuits shown in Figures 1 to 4, the arrangement shown has been made as simple as possible in order not to complicate the description of the invention by irrelevant circuit details which will be readily familiar to any one skilled in the art. The toll lines therefore are shown connected over an operators cord circuit since the nature of the invention may be ascertained in a simpler manner in this case than in the case where automatic switches are used.

Figure 1 shows the signalling equipment at the incoming end of toll line 101 which is connected to an operators cord circuit shown in Figure 2. The operator in this case is a switching operator who connects through to any required exchange requested by the operator at the distant end of the line 101. Figure 3 shows the signalling equipment at the outgoing end of line 301 which is operated on the same basis as the line 101. Figure at shows the equipment associated with a repeater in order that a connection between the lines 101 and 301 may be made by way of repeaters when necessary.

Operation of the arrangements The method of working used by the operators is as follows The operator at the distant end of the line 101 plugs into the line and thus lights the switching operators lamp 201. The switching operator then enters the circuit by throwing her key 202 and plugs the line through i to the required exchange. In most cases this will be over comparatively short lines to local subscribers and no repeater will be needed. In this case when the subscriber replies a signal is sent back over the line 101 to extinguish the distant supervisory lamp, thus to inform the operator. When the subscriber releases at the end of a call a further signal is sent back to light the supervisory lamp and the distant operator then pulls out the plug to release the connection. The removal of the plug sends back a signal to the switching operator of Figure 2 by lighting lamp 201 and the operator then pulls out her plug and the line is ready for another call.

If the request from the originating operator involves extending the call over another long line the switching operator plugs into this line and the train of operations are repeated, another operator being called at the distant end, the subscriber replying and eventually releasing and then the originating operator and the switching operators tak ing down as before. The line 301 used in this case will of course be available also for local calls, so that a control operator similar to the operator at the distant end of the line 101 as well as the switching operator may pick up the line 301 and complete calls over it. Figure 8, therefore, with the omission of the special relays used for introducing the cord circuit repeater, represents also the equipment at the outgoing end of line 101, while Figure 1 gives a good idea of the equipment which will be located at the distant end of line 301.

Consider now the method of working in the case where the switching operator of Figure 2 is replaced by automatic apparatus. In this case the distant operator on 101 plugs has the line at this prepares the automatic.

apparatus. She then dials or key-sends to set up a connection either to a subscriberv in the local area or to a Subscriber obtained over a distant line such as 301. Supervisory signals are received back from the subscriber in the usual manner, and at the conclusion of the call the originating operator takes down and the automatic apparatus then releases.

Operation without repeaters- ConsideringnoW the detailed operation of the circuit, fourvoice frequency relays 102, 103, 104, and are bridged across the in-.

coming end of line 101 and when these are operated by received pulses ofvoice fro-M quency current theyoperate the corresponding relays 106 to 109." These relaysare asinspection.

sociated with coding relays 110 to 113 Whichare released only when certain combinations of the four voice frequency relay's areoperw ated for a giventime... For this reasonthe coding relays arefinad'e slow to release and are connected in the circuit shown. The operation The four voice frequencies which areused in the signalling apparatus are indicated'by the letters W, X, Y and Z and relays and the required line.

supply circuits which are associated with definite frequencies are m'arked'with these letters. s V g The signalling code is summarized below Cord circuit repeater signal for long line WZ Cord circuit repeater signal for-shortline XZ When the operatorplugs intothe line 101 a shortpulse of the combination is sent and this releases relay :112 and thus locks up relay 114 over a circuit controlled by relay 113, which is therelease relay. Relay 11 1 closes a circuit, over its from contact and the'back contact of 115 to light the lamp 201. a The switching operator then takes'the number of the wanted line and plugs into Vhen the called subscriber replies the supervisory relay 116 is energized and closes a circuit'to energize relay 117. The type of j unct ioi'i-signalling used and hence the connections of relay 116vary Widely, butin all cases some supervisoryrelay is-provided to control the subscribers switch hook;

Relay 117' is arranged to senda pulseof voicefrequency current out of one'combination on to the line Whenever it energizesand Itwill be seen that the cycle of operations is just the same as in the case described above where a switching operator is used in place of the automatic apparatus.

supervisory lamp.

of this circuit will be clear upon plug fromthe extinguishes 201.

to send adifierent'p ulse every timeiit Vite- -leases, these pulses being used to control the distant supervisorylamp. The" circuit effecting this consists o frelay 11 119, 120; 121V I i and 122. Theenergization of relay 117 opens the circuit ofrelay 118 but this is slow to re-' lease and thus a circuitis maintained fora short timeover its front contactto energize relay 120; Relay 120" energizes relay 122 over an obyious circuitand connects the" fre- I 7 With busy condltlon. At the concluslonot 1 the conversation, relay116 releases, thejdistant supervisory lamp lights,'the originating operator takes .down and thus a pulse of voice frequency current is received to o'perate lease the connection. The removal fof the jack releases 115 and thus The above description assumes that no cord circuitrepeater W as'necessa1"y. Similar conditions forlline 301' will-now be-described' This is the case when301'ispickedup by an originating operator directly and not over another long line.

Thecord circuit in thiscase will not bethe same as'that shown in 202 butin every case a sleeve circuitiwill'be avail able to energize the relayand also a form of supervisory relay willbepresentinthe cor,d. f The par- 'ticular arrangements postulated (are shown [in the drawings but it will be clear that; any

lmown metl1od of signalling can be use'ol.

The ack 203, or more probably. anothena'ck fin parallelwith203 on the'other. operators position, will be. picked upto call the distant switching operator or lto prepare, distant the line; *These sending relays are operated when the lineis released to send the combination'WY'to give a release signal'at the dis-' tant end. The trelays308 to 317 are similar 115, automatic apparatus. This will energize re 3 lla'y 302 and'will cause the circuit consisting j at relays 303, 304, 305, 306'and 307 to func v tioninprecisely the. same way as the correspending relays in Figure 1. A shortpul'se.

of the combination WX is thus 'sent out to the corresponding, reut stnrfiigut 1,

relay 316 being released bythecombination *WX rec'eived ever the line to' .eiz-tingui'sl ftlie supervisory lamp and relay 317 being 'released by the combinationW-Y to light the 90, relays 102 and 104. This releases 113 and I hence 114, and this closes the circuit for lamp 201 over the front contact ofjr'elay 115 and thus tells the switching operator torei the tip and ring to energize the supervisory long lines.

relay corresponding to relay 116.

Operation with repeaters The energization of 318 when the called subscriber replies also energizes 319 for a short time until the slow release relay 320 releases. Relay 319 during energization places voice frequency currents back on to the jack 203. This current will be at a very low level and will occur only for a very short time so that it will not be noticed appreciably by the called subscriber who is Waiting on the line. Its function is to operate the signalling apparatus of any other connected toll line in order to introduce the cord circuit repeater. Thus if line 301 is connected to a local circuit nothing happens. If, however, the connection is to another long line such as 101 the signalling relays in this line are operated. Line 101 is assumed to be a long line which has'a high attenuation and which therefore needs a repeater when connected to any other It is provided consequently with two relays 110 and 111 which respond to either signalling code. Line 301 is assumed to be a short line and therefore sends out combination XZ. If 101 were also a short line relay 110 would not be provided and therefore no repeater would be inserted, but since it is a long line it responds to either i XZ or VZ, the release of either 110 or 111 thus functioning to lock up 123. Relay 123 places battery on the starting circuit of the finder switch 402; this energizes the high resistance relay 401 to start all the free finder switches such as 402 hunting for a line. Vfhen a finder reaches the line, relay 404 in its associated repeater circuit is energized. This relay opens the stepping magnet 405 to stop the finder. It also shunts relay 401 and the latter falls off to stop the other finders hunting. Relay 404 places earth on a circuit to start the network finder 406 and the other line finder 407 searching for network 440 and for line 301 respectively. The stepping magnet 408 on the network finder is energized over an obvious circuit and the finder 406 hunts until the first of the terminals marked on brush 0 of 402 is reached. At thispoint the transformer 448 is short circuited and the current in its primary is thus increased sufficiently to operate the voice frequency relay 409. This in turn operates 410 and thus prcpares the test circuit which enables the switch to hunt for a free network in the group. The free network is indicated by battery potential on brush and this energizes relay 411 to open the stepping circuit. The low resistance relay 411 renders the circuit busy. Any standard circuit stopping the switch when all networks in the'group are busy, can be used (e. g. last contact to have permanent battery).

Meanwhile switch 407 has been hunting for line 301, the stepping magnet 412 being energized over a circuit via the contacts of relays 413, 414 and 415 to ground from relay 404. The ground from relay 404 also closes the filament circuit of the repeater.

The line 301 is marked on brushes (Z and e of 407 by the voice frequency current applied from the source 416 through the transformer 417 to brushes cl and e of 402 and thence to the line circuit of 101, plug 204, jack 203, line circuit of 301. hen the correct terminals are found relay 418 energizes relay 414 to open the stepping circuit and the repeater is then completely connected.

No separate network selector is shown on this side in order to eliminate the method of operation which would be used if individual networks for each line were provided.

The use of the transformers 448 and 417 to control the hunting of 406 and 407 in order to avoid cross connection between hunting switches. The voice frequency current in the primary circuit will only increase sutliciently to operate the relays on a complete short circuit and not on a cross connection. Other means are available for carrying this out on finder 406, but the described method is probably the most satisfactory way in the case of switch 407. If the transmission bridgesin Figures 1, 2 and are of the repeating coil type an effective short circuit can still be obtained by a proper polling of i the connections.

The test relay 413, and relay 414 lock up relay 415 to maintain the stepping circuit open after the release of 414 and also to switch in the cord circuit repeater. The latter is done by earth from 415 over the contact of relay 411 to brush 9 of finder 402, to relay 419, and to relay 420. Relays 419 and 420 remove the voice frequency testing circuit of transformer 417 from the line and connect in the repeater at the same time removing short circuits designed to prevent one repeater from singing. Earthover brush 9 of switch 402 energizes relay 124 to remove the signalling apparatus from line 101 (in order to reduce imbalances and to prevent false operation of the apparatus by high level currents from the repeater) and connects through. the line circuit from the operators position to the monitoring windings 421 and 422 of the repeater.

The operator can thus listen and talk over the circuit just as if the repeater were not connected. In fact she will be unaware that a repeater has been inserted. In a similar way the signalling apparatus in Figure 3 is cut out by energization of relay 321, by earth from contact of relay 413.

The repeater consists of two amplifiers 423 and 424 together wlth two hybrid coils and 426 of which the windings 421 and 422 the selection of the repeater IS in progress.

form a )art. The 0 aeration of this arran 'ement is familiar to those skilled in the art.

l-Vhen the repeater is insertedthe voice frequency signals coming in from 301' are transmitted direct through the repeater and are no longer relayed over the switching channel of Figure 2. The signal which indicates the reply of the called subscriber is however transmitted over the regular channel. in the wayalready described, during the time that At the end of the'conversation the distant operator releases the circuit by removing her plug. This sendsout a pulse of voicefrequency current which energizes the signalling relays 427 to 435 in the manner described for similar-relays inFigure 1, and thus energizes relay 436. Itwill'be clear that the signalling relays ofFig. 1 couldbe connected in place of relays 4&27-435by providing eritra trunks of switch l02. .Relay 43s maintains earth on a commonlead for ashort time to energize relays 418 and 139. Relay 413 unlocks 415 and removes earth from brush 7 of switch 407 to release relay321. It also closes the circuit of magnet 4:12 overthe oil normal springs and the switch returns to normal. The release of relay 415 removes earth from brush 9 of switch 402 and from relays 419 and 120. The cord circuit repeater thus returns to normal and relay 124 is also released I thus opening the energizing circuit of relay 402. Interference due to tone placed on the talking-circuit is avoided by therelease of relay lO-i or by. choosing the proper timing constants for the different relays.

- The previous energization of relay 24 had released relays 114 and 123. Lamp 201 lights owing to the release of relay 125 which was energized when relay 124' operated. The.

switching operator thenremoves her plug and relay 115 releases and the circuit is ready for anothercall. v

The removal of the plug from jack 203 sends out a releasing signal over line 301 in the manner already described.

The invention enables oneto use gain regulation apparatus for controlling the amplit'cation of the repeaters. Forexample, this may be done by means of a series of marginal relays in the circuit line repeater controlled I by the line equipment apparatus TLl' (and TLO) or by means of attenuatingpads con nected in the lead from the line to the repeater equipment REP. In another'instance the gain regulation may beunder the control of a local operator and in this case theuoper ,ation may be carried out over a connecting switch RP or the line equipment TLl or TLO by means of alternating current (e. g. :v'oicev frequency). The latter method obviates the need for special switches to connect up the repeater and the local cord circuit. "Gain control may also be in the hands'of the distant operator by means ofthe signalling equip- 1 ment TLl. I y I In a further modification the circuit may .bearrangedto release also the line equipment apparatus TLl and TLO, thus improving the balance of the circuit. A'group of vo ce frequency relays provided in-the repealter equipment REP can then be arranged ii to adjust the gain regulation apparatus by means of alternating current received either from a local operator in the case of manual switching, orfrom a distant operator in the case of .automatic switching. This latter relay group would also be used to release the connection.

be provided under control either of the originating operator 'or the switching operator.

Gain control by voice frequency means can I Either operator may be provided with a key or-keys which place a certain combination or z...

a numberof combinations of voice frequency currents upon. the calling circuit to operate the'relays102, 103, 104, and 105 or the relays 427, 428,429 and 430. 'This will release a I relay. similar torelays 110%113 or 435 and will operate they gain control circuits in the repeater. If the signalling equipment of Fig. 1 is used this, of course, will be done'over a brush of finder 402. I

In the abovearrangement it will benoticed that .theiconnection of the cord circuit re d peaters is controlled entirely by the line the connection will be'fam'iliar.

in the casewhere' the connectingjcircuitof Fig. 2 consists of automatic equipments it Y mon group of repeaters for a large number of,

. tures andvarious' methods of carrying out will be clear that the operationof relay 124' or any similar part of the circuit could'be used to release this apparatus and make it available for other calls.

'Although the inventionhas been described in connection with embodiments wherein alternating current such as volce frequency currents are used for controlling thejinsertion of a repeater in a transmission circuit it will beclear to those skilled in the art that other signalling currents may be usedjfor the above purposes,for instancedirect cur rent or direct current impulses may be em the connecting circuit permits. *mo'dulated or interrupted alternatingcurrents may also be used with considerableadvantages lIl $01116 0&S9S.-

ployed-instead of; alternating current when I Likewise Claims: Y

1. In a telephone system, lines, ineansfor interconnecting said lines, a repeater, and means controlled over an established connection between two of said lines for inserting said repeater in said established connection.

2. In a telephone system, lines each including a pair of talking conductors, means for interconnecting said lines, a repeater, and means controlled over the talking conductors of an established connection between two of said lines for inserting said repeater in said established connection.

3. In a telephone system, lines, means as sociated with each of said lines for selectively'transmitting and receiving alternating currents of different frequencies over the talking conductors thereof, means for interconnecting said lines, a repeater, and means selectively responsive to said alternating currents controlled over the talking conductor of an established connection between two of said lines for inserting said repeater in said established connection.

i. In a telephone system, lines of different character, means associated with each of said lines for transmitting alternating currents corresponding to the characteristics of said lines over the talking conductors thereof, means for interconnecting said lines, re-

peaters of diiferent characteristics, and

means responsive to said alternating currents controlled over the talking conductors of an established connection between two of said lines for selecting and inserting one of said repeaters in said established connection. 5. In a telephone system, lines of different character, means associated with each of said 'lines for transmitting alternating currents corresponding to the characteristics of said lines over the talking conductors thereof, repeaters of different characteristics, means for interconnecting said lines, and means responsive to said alternating currents controlled over the talking conductors of an established connection between two of said lines for selecting an appropriate repeater, adjusting said selected repeater, and for inserting said selected and adjusted repeater in said established connection.

6. In a telephone system, lines of different character, means associated witl'i'each of said lines for transmittii'ig and receiving alternating currents of different frequency over the talking conductors thereof, each said means being arranged to transmit alternat ing .currents corresponding to the charact ristics of the said associated line, means for interconnecting said lines, repeaters of chi ferent' chracteristics, andmeans responsive to alternating currents transmitted by one of said lines over an established connection to another of said lines and received-by the said other said line for selecting an appropriate one of said repeaters and inserting it in said established connection.

7. In a telephone system, lines each including a pair of talking conductors, means for interconnecting said lines, a plurality of repeaters, a switch for selecting one of said repeaters controlled over the talking conductors of an established connectionbetween two of said lines, and means for inserting said selected repeater in said established connection.

8. In a telephone system, lines each including a pair of talking conductors, means for interconnecting said lines, a plurality of repeaters, a switch for selecting one of said repeaters, means controlled over the talking conductors of an established connection between two of said lines for starting said switch, and means for inserting said selecting repeater in said established connection.

9. In a telephone system, lines each including a pair of talking conductors, means for interconnecting said lines, a plurality ofrepeaters, an incoming and an outgoing switch for each of said repeaters, means controlled over the talking .conductors of an established connection between two of said lines for starting said incoming switches to select one of said repeaters, means controlled over the talking conductors of an established connection between two of said lines for stopping the outgoing switch of a selected repeater, and means for inserting said selected repeater in said established connection.

10. In a telephone system, lines each including a pair of talking conductors, means for interconnecting said lines, a plurality of repeaters, incoming and outgoing switches at the incoming and outgoing connections of said repeaters, means controlled over the talking conductors of an established connection between two of said lines for starting said incoming switches to select one of said repeaters, a plurality of adjusting networks, an auxiliary switch for selecting one of said networks and connecting it to a selected one of said repeaters, means controlled over the talking conductors of an established connection between two of said lines for stopping said outgoing switches, and means for inserting said selected repeater in said established connection.

11. In a telephone system, lines each including a pair of talking conductors, means individual to each of said lines for transmitting and receiving alternating currents over different frequencies, means for interconnecting said lines, a plurality of repeaters, an incoming and an outgoing switch for each of said repeaters, alternating current responsive means controlled over the talking conductors of an established connection between two of said lines for starting said in coming switches to select one of said repeaters, alternating current responsive means controlled over the talking conductors of an established connection between two of said.

lines for stopping the outgoing switch of a selected repeater, and means for inserting said selected repeater in said established connection.

12. In a telephone system, lineseach including a pair of talking conductors, means individual to each of said lines for transmitting and receiving alternating currents of difierent frequencies, means for intercom necting said lines, a plurality of repeaters, an incoming and an outgoing switch for each of said repeaters, alternating current responsive means controlled'over the talking conductors of an established connection between two of said lines for starting said 'incoming switches to select one of said repeaters, means for stoppingthe outgoingswitch of a selected repeater, said-stopping means comprlslng a relayin clrcult wlth a source .of alternating current and one winding of a transformer, the other winding of said transformer being included in a circuit 7 adapted to be closed through the talking conductors of an established connection between two of sald llnes, and means for inserting said selected repeater in said established connection. V p In witness whereof I hereunto subscribe my name this twelfth day of June, 1929.

THOMAS SAMUEL SKILLMAN'. 

